1. Field of the Invention
The present invention relates to a continuously variable transmission (CVT) for traction drives which is used to transmit rotation from an input side to an output side while continuously varying the speed by traction drive in a power transmission device of an automobile, industrial machinery and so forth, and more particularly, to a rotary assembly for traction drives which includes a rolling element having a traction contact surface which exhibits excellent traction characteristics as surface properties.
Various researches have been conducted on CVTs because of their excellent motive power transmission properties and absence of high-speed shock. In particular, researches have been conducted on systems (traction drive systems: rolling systems) that transmit motive power between traction contact surfaces by means of traction oil for the purpose of transmitting large motive power.
Traction drive systems which transmit motive power between traction contact surfaces by means of traction oil have a mechanism applicable to high-power engines. As shown, for example, in FIG. 1, the basic structure of rotary assembly 1 for traction drive type CVTs. Rotary assembly 1 includes two metal rolling elements, namely, two disks (input disk 3 circumferentially fixed on input shaft 2 and output disk 5 circumferentially fixed on output shaft 4), and power roller 6 interposed between the rolling elements and contacted therewith through a traction oil. Power roller 6 has a tiltable roller shaft such that power roller 6 is inclined relative to input and output disks 3 and 5 when the roller shaft tilts. Owing to the inclination of power roller 6, the contact between power roller 6 and input and output disks 3 and 5 shifts. This changes the ratio of the torque radius of input disk 3 to that of output disk 5 to thereby continuously change the transmission ratio. A half toroidal type CVT is one of traction drive CVTs.
FIG. 42 illustrates a toroidal type CVT which includes input shaft 101 and output shaft 102 coaxial with input shaft 101 and rotatable relative thereto. An engine torque is supplied via fluid coupling 103 to input shaft 101. Forward and reverse input gears 104 and 105 are disposed on input shaft 101 so as to make a unitary rotation therewith. Two input disks 106 and 107 are drivingly connected with each other through hollow shaft 112 extending parallel to input shaft 101. Two output disks 108 and 109 are arranged in an opposed relation to input disks 106 and 107 and connected with each other via shaft 111 extending inside hollow shaft 112. Drive plate 110 is disposed between input disks 106 and 107 and drivingly connected therewith by loading cams 114 and 115. Gear 113 integrally formed with drive plate 110 is engageable with forward input gear 104. Two power rollers 116 are disposed between opposed input and output disks 106 and 8 and in friction contact with traction contact surfaces 106a and 108a thereof. Two power rollers 117 are disposed between opposed input and output disks 107 and 109 and in friction contact with traction contact surfaces 107a and 109a thereof. Power rollers 116 and 117 are rotatable about axes 116a and 117a thereof to transmit the torque from input disks 106 and 107 to output disks 108 and 109, respectively. Power rollers 116 and 117 are also adapted to offset or swing in directions of axes 116b and 117b extending perpendicular to axes 116a and 117a, respectively. Forward/reverse change mechanism 123 is disposed on final drive shaft 119 disposed coaxially with input shaft 101. Gear 120 rotatably supported on final drive shaft 119 is engageable with reverse input gear 105. Forward/reverse change mechanism 123 includes forward clutch 121 connecting final drive shaft 119 with output disk 109 and reverse clutch 122 connecting final drive shaft 119 with gear 120. Final drive shaft 119 is also connected with output shaft 102 via chain transmission mechanism 124. Such a toroidal type CVT is disclosed in Japanese Patent Application First Publication No. 62-251559.
The rolling elements, namely, input disk 3, output disk 5, power roller 6, of rotary assembly 1 shown in FIG. 1, are required to have excellent traction characteristics and high rolling fatigue life characteristics under high temperature and high bearing pressure. In addition, in consideration of the future burden on the environment, it is necessary that vehicle weight be reduced to achieve further improvement of fuel economy. In order to accomplish this, the unit size must be reduced, and in the case of units of the same size, it is necessary to increase the motive power that can be transmitted.
In consideration of the problems of the prior art described above, the object of the present invention is to provide a traction drive rotary assembly capable of transmitting large motive power and having excellent traction characteristics.
According to one aspect of the present invention, there is provided a rotary assembly for traction drives, comprising:
a plurality of rolling elements having a rotation axis and traction contact surfaces around the rotation axis and associating with each other to transmit a motive power between the rolling elements via a traction oil film formed between the traction contact surfaces;
at least one of said traction contact surfaces having a microstructure with irregularities which sizes are larger than a thickness of the traction oil film.
According to a further aspect of the present invention, there is provided a rotary assembly for traction drives comprising a plurality of rolling elements having a rotation axis and traction contact surfaces around the rotation axis and associating with each other to transmit a motive power between the rolling elements via a traction oil film formed between the traction contact surfaces, at least one of said traction contact surfaces having a microstructure with irregularities which sizes are larger than a thickness of the traction oil film, wherein the traction contact surface is formed by a process, the process comprising:
subjecting a surface of the rolling element to shot peening to form recesses and projections therein; and
subsequent to the shot peening, machining the projections by either one of lapping, mirror polishing, super finishing, cutting and grinding to form the top-flat lands and thus produce the traction contact surface.
According to a still further aspect of the present invention, there is provided a rotary assembly for traction drives comprising a plurality of rolling elements having a rotation axis and traction contact surfaces around the rotation axis and associating with each other to transmit a motive power between the rolling elements via a traction oil film formed between the traction contact surfaces, at least one of said traction contact surfaces having a microstructure with irregularities which sizes are larger than a thickness of the traction oil film, the microstructure being represented by an unfiltered primary profile curve including alternately arranged recesses and top-flat lands, wherein the traction contact surface is produced by a process, the process comprising:
forming recesses each having a depth of 10 xcexcm or less at equal intervals in a surface of the rolling element to form alternate arrangement of the recesses and projections between the recesses; and
subsequent to the forming, machining the projections such that a height difference between a top of each top-flat land and a bottom of each recess is within a range of 0.5-2.5 xcexcm, to produce the traction contact surface.
According to a still further aspect of the present invention, there is provided a rotary assembly for traction drives comprising a plurality of rolling elements having a rotation axis and traction contact surfaces around the rotation axis and associating with each other to transmit a motive power between the rolling elements via a traction oil film formed between the traction contact surfaces, at least one of said traction contact surfaces having a microstructure with irregularities which sizes are larger than a thickness of the traction oil film, the microstructure being represented by an unfiltered primary profile curve including alternately arranged recesses and top-flat lands, wherein the traction contact surface is produced by a process, the process comprising:
making a surface roughness of a surface of the rolling element a ten-point mean roughness (Rz) of 100 nm or less; and
subsequent to the making, forming recesses each having a depth of 0.5-2.5 xcexcm at equal intervals in the surface of the rolling element to form alternate arrangement of the recesses and top-flat lands between the recesses and thus produce the traction contact surface.